This invention is directed to an optical system which provides well-collimated light of excellent uniformity of intensity so that it is particularly useful for an exposure system and, with a beam splitter, it is useful for concurrent both-side exposure of printed circuit boards or other systems having photosensitive material thereon. As an exposure system, the optical design is useful for either single-sided exposure or double-sided exposure. Furthermore, the characteristics of the beam make the optical system particularly suitable for use as a solar simulator. The optical design provides good collimation even with a short optical path and good uniformity of the intensity of the beam for uniform exposure.
Modern electronic design includes the reduction in physical size of assembly by employing systems of smaller size. Concurrent with this, the interconnection of electronic systems has been made more compact by employing printed circuit boards of continually more compact arrangement. The other arts have improved, including the exposure definition of the photosensitive material, the making of photo-exposure masks of continually finer definition, and the control of the chemical etching procedure itself. In order to take advantage of these advances and to maximize the advantages of these advances in the other arts, advances in the optical exposure of the photosensitive resist must be made. The exposure must be substantially uniform over this exposure area to provide substantially uniform development characteristics. Furthermore, the illumination provided for the exposure must be well-collimated to provide a sharp exposure edge at each edge in the mask.
The exposure system of this invention is designed to satisfy those needs and also to provide for large area exposure and for double-sided exposure for those cases where photosensitive material and masks are provided on both sides of the board. Furthermore, the exposure system is well-suited for being incorporated into an automated system.